Method of fabricating a photomask

ABSTRACT

A method of fabricating a photomask comprising providing a photomask blank including a phase shifting layer, a first light blocking layer, a first resist layer, a second light blocking layer and a second resist layer stacked sequentially in this order on a substrate, forming second resist patterns, forming second light blocking patterns, forming first resist patterns, forming first light blocking patterns and phase shifting patterns, removing the first resist patterns, and selectively removing at least one of the first light blocking patterns, wherein the second resist layer has a thickness such that all of the second resist layer is removed while the first resist layer is patterned for exposing the second light blocking layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/064,348 filed on Mar. 8, 2016, which claimspriority under 35 U.S.C 119(a) to Korean Patent Application No.10-2015-0154958, filed on Nov. 5, 2015, which is incorporated herein byreference in its entirety.

BACKGROUND 1. Technical Field

Various embodiments of the present disclosure relate to a method offabricating a photomask.

2. Related Art

Highly integrated semiconductor devices exhibit improved operation speedand lower power consumption. Various advanced process technologies havebeen proposed for reducing the minimum feature size of circuit patterns,such as interconnection patterns, and contact hole patterns employed forelectrically connecting the interconnection patterns. For example,various advanced photolithography technologies have been used forforming fine patterns. Generally, photolithography processes employphotomasks, exposure apparatuses and resist materials all of which areimportant in minimizing the size of the circuit patterns.

Generally, forming accurate photomask patterns on a mask substraterequire to accurately pattern a resist layer of a photomask blank.Generally, a phase shift photomask blank may include a phase shiftinglayer, a light blocking layer and a resist layer which are stackedsequentially on a substrate. Typically, the resist layer is patternedfor forming resist patterns, whereas the light blocking and the phaseshifting layers are patterned using the resist patterns for forminglight blocking patterns and phase shifting patterns, respectively. Insuch a case, the pitch sizes of the light blocking patterns and thephase shifting patterns are determined by the pitch size of the resistpatterns. The resist patterns may act as etch buffers or etch maskswhile an etch process for patterning the light blocking layer isperformed. Thus, according to existing processes, the resist layershould be formed to have at least a sufficient thickness foraccommodating the above processes. Increasing the thickness of theresist layer generally may improve the accuracy of the light blockingand the phase shifting patterns, however, it may make it more difficultto accurately pattern the resist layer. Accordingly, it is generallydifficult to form accurate light blocking and phase shifting patterns.

SUMMARY

Various embodiments are directed to methods of fabricating photomasks.

According to an embodiment, there is provided a method of fabricating aphotomask. The method includes providing a photomask blank having aphase shifting layer, a first light blocking layer, a first resistlayer, a second light blocking layer and a second resist layer which arestacked sequentially in this order on a substrate. The second resistpatterns are formed by patterning the second resist layer. The secondlight blocking patterns are formed by patterning the second lightblocking layer using an etch process employing the second resistpatterns as etch masks. The first resist patterns are formed bypatterning the first resist layer using an etch process employing thesecond light blocking patterns as etch masks. The first light blockingpatterns and the phase shifting patterns are formed by patterning thefirst light blocking layer and the phase shifting patterns by patterningthe first light blocking layer and the phase shifting layer using anetch process employing the first resist patterns as etch masks. Thefirst resist patterns are then removed. At least one of the first lightblocking patterns is selectively removed. The second resist layer has athickness such that all of the second resist layer is removed while thefirst resist layer is patterned for exposing the second light blockinglayer.

According to other embodiment, there is provided a method of fabricatinga photomask. The method includes providing a photomask blank having afirst light blocking layer, a first resist layer, a second lightblocking layer and a second resist layer which are stacked sequentiallyon a substrate. The second resist patterns are formed by patterning thesecond resist layer. The second light blocking patterns are formed bypatterning the second light blocking layer using an etch processemploying the second resist patterns as etch masks. The first resistpatterns are formed by patterning the first resist layer using an etchprocess employing the second light blocking patterns as etch masks. Thefirst light blocking patterns by patterning the first light blockinglayer using an etch process employing the first resist patterns as etchmasks. The first resist patterns are then removed. The second resistlayer has a thickness such that all of the second resist layer isremoved while the first resist layer is patterned for exposing thesecond light blocking layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure will become more apparentin view of the attached drawings and accompanying detailed description,in which:

FIG. 1 is a cross-sectional view of a phase shift photomask blank,according to an embodiment of the present disclosure;

FIGS. 2 to 7 are cross-sectional views illustrating a method offabricating a phase shift photomask using the phase shift photomaskblank shown in FIG. 1;

FIG. 8 is a cross-sectional view of a binary photomask blank accordingto an embodiment of the present disclosure; and

FIGS. 9 to 13 are cross-sectional views illustrating a method offabricating a binary photomask using the binary photomask blank shown inFIG. 8.

DESCRIPTION OF SPECIFIC EMBODIMENTS

It will be understood that although the terms first, second, third andso on may be used herein to describe various elements, these elementsshould not be limited by these terms. These terms are only used todistinguish one element from another element. Thus, a first element insome embodiments could be termed a second element in other embodimentswithout departing from the teachings of the present disclosure. It willalso be understood that when an element is referred to as being located“on,” “over,” “above,” “under,” “beneath,” “below,” “side,” or “aside”another element, it may directly contact the other element, or at leastone intervening element may be present therebetween. Accordingly, theterms such as “on,” “over,” “above,” “under,” “beneath,” “below,”“side,” “aside,” and the like that are used herein are for the purposeof describing only a position relationship of two elements and are notintended to limit the scope of the present disclosure. It will befurther understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

FIG. 1 is a cross-sectional view of a phase shift photomask blank 100according to an embodiment.

Referring to FIG. 1, the phase shift photomask blank 100 may include aphase shifting layer 120, a first light blocking layer 130, a firstresist layer 140, a second light blocking layer 150 and a second resistlayer 160 all of which are stacked sequentially on a substrate 110. Inan embodiment the order of the layers may be as shown in FIG. 1.

The substrate 110 may be or include a light transmitting material, forexample, a quartz material, a glass material, a silicon material, asilicon nitride material or a silicon oxynitride material.

The phase shifting layer 120 may be disposed on the substrate 110. Thephase shifting layer 120 may be or include any suitable material. In anembodiment, the phase shifting layer 120 may be or include a molybdenumsilicide (MoSi) layer. The phase shifting layer 120 may shift a phase ofa light passing therethrough by about 170 degrees to about 190 degrees.That is, a phase of a light penetrating all of the phase shifting layer120 and the light transmitting substrate 110 may precede a phase of alight penetrating only the light transmitting substrate 110 by about 170degrees to about 190 degrees. The phase shifting layer 120 may have alight transmittance of from about 4% to about 50%.

The first light blocking layer 130 may be disposed on the phase shiftinglayer 120. The first light blocking layer 130 may be or include anysuitable material. For example, the first light blocking layer 130 maybe or include a chrome (Cr) layer, an aluminum (Al) layer, a tantalum(Ta) layer or a titanium nitride (TiN) layer. The first light blockinglayer 130 may have a light transmittance of at most 5%.

The first resist layer 140 may be disposed on the first light blockinglayer 130. The first resist layer 140 and the second light blockinglayer 150 may act as etch buffer layers while the first light blockinglayer 130 is etched. Thus, at least the first resist layer 140 shouldhave a sufficient thickness T1 so that the first resist layer 140remains even after the first light blocking layer 130 is etched. Thatis, an initial thickness (i.e., the thickness T1) of the first resistlayer 140 may be determined so that the first resist layer 140 remainsto have a certain thickness even after the first resist layer 140 isexposed to an etch process for patterning the first light blocking layer130. The initial thickness of the first resist layer 140 may be greaterthan the certain thickness of the remaining first resist layer after thefirst light blocking layer 130 is patterned. In an embodiment, thethickness T1 of the first resist layer 140 may be at least 800angstroms.

The second light blocking layer 150 may be disposed on the first resistlayer 140. As described above, the second light blocking layer 150 andthe first resist layer 140 may act as etch buffer layers while the firstlight blocking layer 130 is etched. The second light blocking layer 150may be etched while the first light blocking layer 130 is etched.Specifically, the second light blocking layer 150 may include a materialthat can be completely removed before an etch process for patterning thefirst light blocking layer 130 is completed. Thus, the second lightblocking layer 150 may include a material having a higher etch rate thanan etch rate of the first light blocking layer 130. In an embodiment,the second light blocking layer 150 may be provided by adding oxygenatoms to the same material employed for the first light blocking layer130. The second light blocking layer 150 may have a smaller thicknessthan a thickness of the first light blocking layer 130.

The second resist layer 160 may be disposed on the second light blockinglayer 150. The second resist layer 160 directly affects the pitch or thewidth of the fine patterns. Thus, the second resist layer 160 may have athickness T2 that is sufficiently thin for forming fine patterns moreaccurately. Accordingly, the thickness T2 of the second resist layer 160may be less than the thickness T1 of the first resist layer 140. Forexample, the thickness T2 of the second resist layer 160 may be fromabout 20% to about 50% of the thickness T1 of the first resist layer140. In an embodiment, in order for forming fine patterns having a widthof from about 15 nanometers to about 25 nanometers, the thickness T2 ofthe second resist layer 160 may be of from about 200 angstroms to about400 angstroms.

FIGS. 2 to 7 are cross-sectional views illustrating a method offabricating a phase shift photomask using the phase shift photomaskblank 100 shown in FIG. 1.

Referring to FIG. 2, after the phase shift photomask blank 100 isprovided, the second resist layer 160 of the phase shift photomask blank100 may be patterned for forming second resist patterns 161 to 165. Thesecond resist layer 160 may be patterned using an electron beam (e-beam)lithography process. The second resist patterns 162 to 165 may be formedin a pattern region 100A, and the second resist pattern 161 may beformed in a frame region 100B. In the present embodiment, pattern imagesof the pattern region 100A may be transferred onto a wafer while theframe region 100B does not include patterns whose images are transferredonto the wafer. The frame region 100B may be disposed to surround thepattern region 100A. The second resist pattern 161 may be formed tocover an entire surface of the second light blocking layer 150 in theframe region 100B. The second resist patterns 162 to 165 may be formedto cover partially the second light blocking layer 150 in the patternregion 100A. Accordingly, portions of the second light blocking layer150 in the pattern region 100A may be exposed by the second resistpatterns 162 to 165.

The second resist patterns 162 to 165 formed in the pattern region 100Amay have the same width. The second resist patterns 162 to 165 may havedifferent widths. For example, the second resist patterns 162 to 165 mayhave two different widths. For example, a width of the second resistpatterns 162 and 165 may be greater than a width of the second resistpatterns 163 and 164 as shown in FIG. 2. More specifically, in theembodiment of FIG. 2, the second resist patterns 163 and 164 maycorrespond to fine patterns having first and a second width W1, W2,respectively. The first width W1 may be equal to or different from thesecond width W2. Even though the second resist patterns 163 and 164 arefine patterns having relatively narrow widths, no collapse of the secondresist patterns 163 and 164 may occur because the second resist patterns163 and 164 are formed to be sufficiently thick to prevent such acollapse.

Referring to FIG. 3, the second light blocking layer 150 may be etchedusing the second resist patterns 161 to 165 as etch masks, therebyforming second light blocking patterns 151 to 155 which are aligned withthe second resist patterns 161 to 165. Portions of the first resistlayer 140 may be exposed by the second light blocking patterns 151 to155 and the second resist patterns 161 to 165. The second light blockingpatterns 153 and 154 may have substantially the same width as the secondresist patterns 163, and 164. That is, the second light blockingpatterns 153 and 154 may have the first and second widths W1, W2,respectively.

Referring to FIG. 4, the first resist layer 140 may be etched using thesecond resist patterns 161 to 165 and the second light blocking patterns151 to 155 as etch masks, thereby forming first resist patterns 141 to145 which are aligned with the second resist patterns 161 to 165 and thesecond light blocking patterns 151 to 155. The etch process for formingthe first resist patterns 141 to 145 may be performed using ananisotropic dry etch process. The anisotropic dry etch process mayemploy an oxygen gas as an etch gas. Since the second resist patterns161 to 165 are thinner than the first resist layer 140, the secondresist patterns 161 to 165 may be removed while the first resist layer140 is etched for forming the first resist patterns 141 to 145. Afterthe first resist patterns 141 to 145 are formed, portions of the firstlight blocking layer 130 may be exposed. The first resist patterns 143and 144 may have substantially the same width as the second lightblocking patterns 153 and 154, respectively. That is, the first resistpatterns 143 and 144 may have the first and second widths W1 and W2,respectively.

Referring to FIG. 5, the first light blocking layer 130 may be etchedusing the second light blocking patterns 151 to 155 and the first resistpatterns 141 to 145 as etch masks, thereby forming first light blockingpatterns 131 to 135 which are aligned with the second light blockingpatterns 151 to 155 and the first resist patterns 141 to 145.Subsequently, the phase shifting layer 120 may additionally be etchedusing the second light blocking patterns 151 to 155 and the first resistpatterns 141 to 145 as etch masks, thereby forming phase shiftingpatterns 121 to 125. Since a thickness of the second light blockingpatterns 151 to 155 is less than a thickness of the first light blockinglayer 130 and an etch rate of the second light blocking patterns 151 to155 is higher than an etch rate of the first light blocking layer 130,the second light blocking patterns 151 to 155 may be removed while thefirst light blocking layer 130 is etched for forming the first lightblocking patterns 131 to 135. After the first light blocking patterns131 to 135 and the phase shifting patterns 121 to 125 are formed,portions of the substrate 110 may be exposed. The first light blockingpatterns 133 and 134 may have substantially the same width as the firstresist patterns 143 and 144, respectively. Similarly, the phase shiftingpatterns 123 and 124 may have substantially the same width as the firstresist patterns 143 and 144, respectively. That is, the first lightblocking pattern 133 and the phase shifting pattern 123 may both havethe first width W1, whereas the first light blocking pattern 134 and thephase shifting pattern 124 may both have the second width W2.

Referring to FIG. 6, the first resist patterns 141 to 145 may be removedto expose top surfaces of the first light blocking patterns 132 to 135in the pattern region 100A and a top surface of the first light blockingpattern 131 in the frame region 100B. A third resist pattern 170 may beformed to cover the first light blocking pattern 131 in the frame region100B. The third resist pattern 170 may be formed to expose the firstlight blocking patterns 132 to 135 and the substrate 110 in the patternregion 100A.

Referring to FIG. 7, the first light blocking patterns 132 to 135 in thepattern region 110A may be removed using an etch process that employsthe third resist pattern 170 as an etch mask. As a result of removal ofthe first light blocking patterns 132 to 135, the phase shiftingpatterns 122 to 125 in the pattern region 110A may be exposed. After thefirst light blocking patterns 132 to 135 are removed, the third resistpattern 170 may be removed. As a result, a phase shift photomaskfabricated by the above processes may include the phase shiftingpatterns 122 to 125 exposed in the pattern region 110A and the phaseshifting pattern 121 covered with the first light blocking pattern 131in the frame region 100B.

FIG. 8 is a cross-sectional view of a binary photomask blank 200,according to an embodiment of the invention.

Referring to FIG. 8, the binary photomask blank 200 may include a firstlight blocking layer 230, a first resist layer 240, a second lightblocking layer 250 and a second resist layer 260 which are stackedsequentially on a substrate 210. The layers may be stacked in the ordershown in FIG. 8.

The substrate 210 may include a light transmitting material, forexample, a quartz material, a glass material, a silicon material, asilicon nitride material or a silicon oxynitride material.

The first light blocking layer 230 may be disposed on the substrate 210.The first light blocking layer 230 may include a chrome (Cr) layer, analuminum (Al) layer, a tantalum (Ta) layer or a titanium nitride (TiN)layer. The first light blocking layer 230 may have a light transmittanceof at most 5%.

The first resist layer 240 may be disposed on the first light blockinglayer 230. The first resist layer 240 and the second light blockinglayer 250 may act as etch buffer layers while the first light blockinglayer 230 is etched. Thus, at least the first resist layer 240 shouldhave a sufficient thickness T3 so that the first resist layer 240remains even after the first light blocking layer 230 is etched. Thatis, an initial thickness (i.e., the thickness T3) of the first resistlayer 240 may be determined so that the first resist layer 240 remainsto have a certain thickness even after the first resist layer 240 isexposed to an etch process for patterning the first light blocking layer230. The initial thickness of the first resist layer 240 may be greaterthan the certain thickness of the remaining first resist layer after thefirst light blocking layer 230 is patterned. In an embodiment, thethickness T3 of the first resist layer 240 may be at least 800angstroms.

The second light blocking layer 250 may be disposed on the first resistlayer 240. As described above, the second light blocking layer 250 andthe first resist layer 240 may act as etch buffer layers while the firstlight blocking layer 230 is etched. The second light blocking layer 250may be etched while the first light blocking layer 230 is etched.Specifically, the second light blocking layer 250 may include a materialthat can be completely removed before an etch process for patterning thefirst light blocking layer 230 is completed. Thus, the second lightblocking layer 250 include a material having a higher etch rate than anetch rate of the first light blocking layer 230. In an embodiment, thesecond light blocking layer 250 may be provided by adding oxygen atomsto the same material employed as the first light blocking layer 230. Thesecond light blocking layer 250 may a smaller thickness than a thicknessof the first light blocking layer 230.

The second resist layer 260 may be disposed on the second light blockinglayer 250. The second resist layer 260 may directly affect the pitch orwidth of the fine patterns. Thus, the second resist layer 260 may have athickness T4 that is sufficiently thin for accurately forming finepatterns. Accordingly, the thickness T4 of the second resist layer 260may be less than the thickness T3 of the first resist layer 240. Forexample, the thickness T4 of the second resist layer 260 may be fromabout 20% to about 50% of the thickness T3 of the first resist layer240. In an embodiment, for forming fine patterns having a width of fromabout 15 nanometers to about 25 nanometers, the thickness T4 of thesecond resist layer 260 may be of from about 200 angstroms to about 400angstroms.

FIGS. 9 to 13 are cross-sectional views illustrating a method offabricating a binary photomask using the binary photomask blank 200shown in FIG. 8.

Referring to FIG. 9, after the binary photomask blank 200 is provided,the second resist layer 260 of the binary photomask blank 200 may bepatterned for forming second resist patterns 261 to 265. For example,the second resist layer 260 may be patterned using an electron beam(e-beam) lithography process. The second resist patterns 262 to 265 maybe formed in a pattern region 200A, whereas the second resist pattern261 may be formed in a frame region 200B. In the present embodiment,pattern images of the pattern region 200A may be transferred onto awafer. By contrast, the frame region 200B does not include patternswhose images are transferred onto the wafer. The frame region 200B maybe disposed to surround the pattern region 200A. The second resistpattern 261 may be formed to cover an entire surface of the second lightblocking layer 250 in the frame region 200B. The second resist patterns262 to 265 may be formed to cover partially the second light blockinglayer 250 in the pattern region 200A. Accordingly, portions of thesecond light blocking layer 250 in the pattern region 200A may beexposed by the second resist patterns 262 to 265.

The second resist patterns 262 to 265 formed in the pattern region 200Amay have the same width. The second resist patterns 262 to 265 may havedifferent widths. The second resist patterns 262 to 265 may have twodifferent widths. For example, a width of the second resist patterns 262and 265 may be greater than a width of the second resist patterns 263and 264. In the present embodiment, the second resist patterns 263 and264 may correspond to fine patterns having first and second widths W3and W4, respectively. The first width W3 may be equal to or differentfrom the second width W4. Even though the second resist patterns 263 and264 are fine patterns having relatively narrow widths, no collapse ofthe second resist patterns 263 and 264 may occur because the secondresist patterns 263 and 264 are formed to be sufficiently thick toprevent such collapse.

Referring to FIG. 10, the second light blocking layer 250 may be etchedusing the second resist patterns 261 to 265 as etch masks, therebyforming second light blocking patterns 251 to 255 which are aligned withthe second resist patterns 261 to 265. Portions of the first resistlayer 240 may be exposed by the second light blocking patterns 251 to255 and the second resist patterns 261 to 265. The second light blockingpatterns 253 and 254 may have substantially the same width as the secondresist patterns 263 and 264. That is, the second light blocking patterns253 and 254 may have the first and second widths W3 and W4,respectively.

Referring to FIG. 11, the first resist layer 240 may be etched using thesecond resist patterns 261 to 265 and the second light blocking patterns251 to 255 as etch masks, thereby forming first resist patterns 241 to245. The first resist patterns 241 to 245 may be aligned with the secondresist patterns 261 to 265 and the second light blocking patterns 251 to255. The etch process for forming the first resist patterns 241 to 245may be performed using an anisotropic dry etch process. The anisotropicdry etch process may employ an oxygen gas as an etch gas. Since thesecond resist patterns 261 to 265 are thinner than the first resistlayer 240, the second resist patterns 261 to 265 may be removed whilethe first resist layer 240 is etched for forming the first resistpatterns 241 to 245. After the first resist patterns 241 to 245 areformed, portions of the first light blocking layer 230 may be exposed.The first resist patterns 243 and 244 may have substantially the samewidth as the second light blocking patterns 253 and 254, respectively.That is, the first resist patterns 243 and 244 may have the first andsecond widths W3 and W4, respectively.

Referring to FIG. 12, the first light blocking layer 230 may be etchedusing the second light blocking patterns 251 to 255 and the first resistpatterns 241 to 245 as etch masks, thereby forming first light blockingpatterns 231 to 235. The first light blocking patterns 231 to 235 may bealigned with the second light blocking patterns 251 to 255 and the firstresist patterns 241 to 245. Since a thickness of the second lightblocking patterns 251 to 255 is less than a thickness of the first lightblocking layer 230 and an etch rate of the second light blockingpatterns 251 to 255 is higher than an etch rate of the first lightblocking layer 230, the second light blocking patterns 251 to 255 may beremoved while the first light blocking layer 230 is etched for formingthe first light blocking patterns 231 to 235. After the first lightblocking patterns 231 to 235 are formed, portions of the substrate 210may be exposed. The first light blocking patterns 233 and 244 may havesubstantially the same width as the first resist patterns 243 and 244,respectively. That is, the first light blocking patterns 233 and 234 mayhave the first and second widths W3 and W4, respectively.

Referring to FIG. 13, the first resist patterns 241 to 245 may beremoved to expose top surfaces of the first light blocking patterns 231to 235. As a result, a binary photomask fabricated by the aboveprocesses may include the first light blocking patterns 232 to 235disposed to expose portions of the substrate 210 in the pattern region210A and the first light blocking pattern 231 disposed to cover anentire surface of the substrate 210 in the frame region 200B.

The embodiments of the present disclosure have been disclosed above forillustrative purposes. Those of ordinary skill in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the scope and spirit of the presentdisclosure as disclosed in the accompanying claims.

What is claimed is:
 1. A method of fabricating a photomask, the methodcomprising: providing a photomask blank including a phase shiftinglayer, a first light blocking layer, a first resist layer, a secondlight blocking layer and a second resist layer stacked sequentially inthis order on a substrate; forming second resist patterns by patterningthe second resist layer; forming second light blocking patterns bypatterning the second light blocking layer using an etch processemploying the second resist patterns as etch masks; forming first resistpatterns by patterning the first resist layer using an etch processemploying the second light blocking patterns as etch masks; formingfirst light blocking patterns and phase shifting patterns by patterningthe first light blocking layer and the phase shifting layer using anetch process employing the first resist patterns as etch masks; removingthe first resist patterns; and selectively removing at least one of thefirst light blocking patterns, wherein the second resist layer has athickness such that all of the second resist layer is removed while thefirst resist layer is patterned for exposing the second light blockinglayer.
 2. The method of claim 1, wherein the forming of the second lightblocking patterns is performed by patterning the second light blockinglayer using an anisotropic dry etch process employing an oxygen gas asan etch gas.
 3. The method of claim 1, wherein the forming of the firstresist pattern includes removing the second resist patterns during thepatterning of the first resist layer.
 4. The method of claim 1, whereinthe selective removing of at least one of the first light blockingpatterns includes: forming a third resist pattern that exposes a patternregion of the substrate and covers a frame region of the substrate;removing the first light blocking patterns on the pattern region of thesubstrate; and removing the third resist pattern.
 5. The method of claim1, wherein the first light blocking layer and the second light blockinglayer have a light transmittance of at most 5%, the first light blockinglayer includes a chrome (Cr) layer, an aluminum (Al) layer, a tantalum(Ta) layer or a titanium nitride (TiN) layer, and wherein the secondlight blocking layer is composed of material added oxygen atoms to thesame material employed for the first light blocking layer.
 6. A methodof fabricating a photomask, the method comprising: providing a photomaskblank including a first light blocking layer, a first resist layer, asecond light blocking layer and a second resist layer which are stackedsequentially on a substrate; forming second resist patterns bypatterning the second resist layer; forming second light blockingpatterns by patterning the second light blocking layer using an etchprocess employing the second resist patterns as etch masks; formingfirst resist patterns by patterning the first resist layer using an etchprocess employing the second light blocking patterns as etch masks;forming first light blocking patterns by patterning the first lightblocking layer using an etch process employing the first resist patternsas etch masks; and removing the first resist patterns, wherein thesecond resist layer has a thickness such that all of the second resistlayer is removed while the first resist layer is patterned for exposingthe second light blocking layer.
 7. The method of claim 6, wherein theforming of the second light blocking patterns is performed by patterningthe second light blocking layer using an anisotropic dry etch processthat employs an oxygen gas as an etch gas.
 8. The method of claim 6,wherein the forming of the first resist pattern includes removing thesecond resist patterns during the pattering of the first resist layer.9. The method of claim 6, wherein the first light blocking layer and thesecond light blocking layer have a light transmittance of at most 5%,the first light blocking layer includes a chrome (Cr) layer, an aluminum(Al) layer, a tantalum (Ta) layer or a titanium nitride (TiN) layer, andwherein the second light blocking layer is composed of material addedoxygen atoms to the same material employed for the first light blockinglayer.